Owning a pool often comes with more responsibilities than new owners often expect when they start their pool journeys. Nearly everyone knows it takes time, purposeful effort, and some non-trivial expenses to keep a pool clean. The pool’s pump and filter system is the cornerstone of its cleanliness, but did you know you’re occasionally supposed to clean out your pump and filter system, too?
The process for cleaning a pool’s pump and filter system can differ depending on the type of filter you use. Pool sand filters are common companions for inground pools, and the cleaning process for these filters is typically known as backwashing.
If you’re not sure how to properly backwash your pool filter, you’ve come to the right place.
In this article, we’ll cover how to backwash sand filters and briefly review the cleaning process for other types of pool filters, which sometimes don’t need to be backwashed at all.
What is backwashing?
When you backwash a pool filter, you’re really just cleaning out any accumulated dirt, debris, chemical build-up, and other gunk that might interfere the filter’s ability to keep your pool’s water clean and enjoyable to swim in.
Here’s the thing, though... you don’t need to backwash every type of pool filter.
There are three common types of pool filters:
- Sand pool filters
- Diatomaceous earth (DE) pool filters
- Cartridge pool filters
Sand and DE filters both require periodic backwashing to flush trapped contaminants out of the system. Cartridge filters work differently and are cleaned by removing and rinsing the cartridge instead.
And let’s be clear, a pool filter is not the same thing as a salt water system, should you have one. Some pump and filter systems include built-in saltwater components, but they each serve different purposes in keeping your pool water clean and balanced.
How often should you backwash a pool filter?
Most sand and DE filters need to be backwashed every one to two weeks during regular pool use, though the exact timing can vary depending on pool conditions and debris levels. The easiest way to know when it’s time to backwash your pool filter is to check the filter’s pressure gauge.
Pressure is usually measured in pounds per square inch, or PSI, in the United States. As gunk
builds up in the filter, water has a harder time flowing through the system, causing the pressure inside the filter to rise.
In most cases, it’s time to backwash your sand or DE filter when:
- The pressure gauge reads 8–10 PSI above normal
- Water flow noticeably weakens
Your filter’s normal operating PSI can usually be found in the manufacturer’s manual. You can also establish a baseline by checking the pressure immediately after cleaning or backwashing the filter.
Once your filter pressure rises above the recommended range, it’s time to clean the filter. The process looks slightly different depending on the type of filter you have.
How to backwash a sand filter
The exact process can vary slightly depending on the manufacturer and filter model, so always check your owner’s manual before beginning. That said, most sand filters follow a similar backwashing process.
To backwash a sand filter:
- Turn off the pump.
- Attach a backwash hose if your system requires one.
- Set the valve to “BACKWASH.”
- Turn pump back on.
- Run the backwash process for 2–3 minutes, or until pool water flowing through the filter’s sight glass is clear.
- Turn pump back off.
- Set the valve to "RINSE" or "CLEAN."
- Turn the pump back on.
- Run the rinse process for at least one minute, or at least until the water in the sight glass is clear.
- Turn off the pump again.
- Remove the backwash hose, if you're using one.
- Set the valve back to "FILTER."
- Turn the pump back on to return to normal filtration.
- Enjoy your clean pool!
Once complete, your filter pressure should return closer to its normal operating range.
How to backwash a diatomaceous earth filter
Backwashing a DE filter is very similar to backwashing a sand filter, but there’s one important additional step: Before turning the system back on for regular use, the filter needs to be replenished with fresh DE powder.
Diatomaceous earth powder and prepared slurry. You'll probably need more than this.
Once the backwash and rinse cycles are complete and the valve has been returned to the “FILTER” position, follow these steps to recharge the filter:
- Lock the filter valve to "FILTER"
- Verify in the filter manual to determine how much DE powder you’ll need.
- Prime the pool pump.
- Open the strainer basket lid.
- Add water to the strainer basket and allow to strain.
- Turn the pool pump back on again.
- Mix the needed amount of DE powder with water to make a plaster-like solution called slurry (it should be pourable, but not quite liquid).
- Slowly pour the slurry directly into the skimmer basket while the pump is running.
- Run the pump for at least half an hour to spread new DE through the filter.
- Enjoy your clean pool!
If you’ve got a push/pull valve instead of a multiport valve on your DE filter, you may need to toggle some switches in slightly different ways. Check your operating manual to make sure you follow the right steps. Regardless of valve type, any DE filter will need to be topped up with more DE after each backwash.
How to backwash a cartridge filter
Psych! You don’t have to backwash a cartridge filter.
You will, however, need to clean the cartridge off when pressure rises 8-10 PSI above normal or water flow weakens.
To clean a cartridge filter:
- Turn off the pool pump.
- Release pressure using the air relief valve.
- Open the filter and remove the cartridge(s).
- Rinse the cartridge thoroughly with a hose, spraying between pleats.
- Soak the cartridge in filter cleaner if oily or heavily dirty (optional).
- Reassemble the filter system.
- Turn the pump back on and release trapped air using the air relief valve until water flows steadily.
Cleaning a cartridge filter usually creates less wastewater than backwashing and is often a fairly straightforward maintenance task for homeowners.
Speaking of wastewater…
What should you do with pool filter backwash water?
Backwashing pushes a lot of water through your pool’s filter system, and it probably won’t be pretty when it comes back out.
This backwash water is considered wastewater, which means you shouldn’t attempt to use 
or reuse it.
Backwash water should not:
- Go back into the pool
- Be used to water grass or landscaping
- Drain into nearby lakes, streams, ponds, or storm drains
Depending on local regulations, improperly disposing of pool wastewater could potentially harm wildlife or contaminate local waterways.
The best way to figure out what to do with backwash water would be to contact your local water authority or municipality. Disposal requirements can vary by county or region, so checking local guidelines is always a good idea.
Final Thoughts
Backwashing and cleaning your pool filter may not be the most exciting part of pool ownership, but it plays a major role in keeping your water clean, clear, and enjoyable to swim in. Understanding how to properly maintain your pool filter, can help your equipment perform more efficiently and potentially extend the life of your pool system over time.
Frequently Asked Questions
How often should you backwash a pool filter?
Most sand and DE pool filters should be backwashed every one to two weeks during regular pool use. However, the best indicator is usually the pressure gauge. If the pressure rises about 8–10 PSI above normal, it’s typically time to clean the filter.
Do cartridge pool filters need to be backwashed?
No. Cartridge pool filters are cleaned differently and do not require backwashing. Instead, the cartridge is removed and rinsed manually when pressure rises or water flow weakens.
What PSI should a pool filter be before backwashing?
Most pool professionals recommend backwashing a sand or DE filter when the pressure gauge reads approximately 8–10 PSI above the filter’s normal operating pressure.
Do you need to add more DE powder after backwashing?
Yes. DE filters need to be recharged with fresh diatomaceous earth powder after every backwash before returning the system to normal operation.
What should you do with pool backwash water?
Pool backwash water is considered wastewater and should not be reused in the pool or drained into nearby waterways. Disposal regulations can vary by location, so it’s best to check with your local water authority for guidance.
From the Author
Pool ownership comes with a learning curve, and sometimes a few surprises for new homeowners. Many people know they’ll need to skim leaves or balance chemicals from time to time, but fewer realize how important the pool’s filtration system is to keeping the water clean and enjoyable to swim in.
I’m Cristian Shirilla, Marketing Manager at River Pools and co-owner of a fiberglass pool installation company in Virginia. Through years of helping homeowners research pool ownership, I’ve seen how overwhelming pool equipment and maintenance topics can sometimes feel at first.
I wrote this article to help homeowners better understand what backwashing a pool filter actually means, along with how to properly clean and maintain different types of pool filters over time.
From the Manufacturer
At River Pools, we understand that many homeowners researching fiberglass pools are also trying to better understand what long-term pool maintenance actually involves.
Questions about pool filters, backwashing, and routine equipment care are some of the most common topics homeowners encounter as they begin learning about pool ownership.
If you’re considering a fiberglass pool and want guidance on pool equipment, maintenance, and backyard planning, the next step is connecting with a trusted independent installer in your area.
Ready to start the conversation?
